The vaccine against yellow fever is again mandatory since January 2008 both on the mainland of Tanzania and the island of Zanzibar.
Sole exception: for passengers from Europe and those who are not passing through an African airport.

PROTECTION AGAINST MALARIA
Tanzania is classified as risk area 3 (high resistance to Nivaquine). Consult your doctor for appropriate prophylaxis. Provide spray or cream to daub your legs in the evening. The risks of contracting malaria are very variable depending on certain factors:

• Altitude. The risk of encountering the Anopheles (malaria vector mosquitoes) decreases rapidly with height. Therefore, prophylaxis against malaria is highly recommended for coastal stays. Conversely, it is inadvisable to take prophylaxis during the ascent of Kilimanjaro.
• Season: Anopheles are most active during the rainy season.

• Protection against water-related risks: it is totally not recommended to drink tap water anywhere whatsoever. The bottled water is available everywhere in Tanzania.
• Protection against the sun: sunglasses, hat, cream. High risk of sunburn (being in safari or on beaches is something alike).